I went on importing my big database through CSV. One question I didn’t manage to find a solution to :

Is it possible to import Categories? I can import all my content, except categories.
By the way, I can’t import any CSV while the “Category Tree” is activated. Linked issue?
And do not ask for logs, I don’t get any, sadly (debug logs activated though).

Sure : https://github.com/ConnieHarper/Omeka2-Plugin-CategoryTree
Just realized I didn’t download this one from Omeka website.
Using latest commit (it didn’t change for 2 years now).
So I understand you are not using categories? The librarian I am working for is telling me that collections have a broader approach than categories. And unfortunately tags won’t allow hierarchical sorting.